RFR: 8318694: [JVMCI] disable can_call_java in most contexts for libjvmci compiler threads [v6]

[Doug Simon]

> This PR reduces the context in which a libjvmci CompilerThread can make a Java call. By default, a CompileThread for a JVMCI compiler can make Java calls (as jarjvmci only works that way). When libjvmci calls into the VM via a CompilerToVM native method, it enters a scope where Java calls are disabled until either the call returns or a nested scope is entered that re-enables Java calls. The latter is required for the Truffle use case described in [JDK-8318694](https://bugs.openjdk.org/browse/JDK-8318694) as well as for a few other VM entry points where libgraal currently still requires the ability to make Java calls (e.g. to load the Java classes used for boxing primitives). We may be able to eventually eliminate all need for libgraal to make Java calls but this PR is a first step in the right direction.

Doug Simon has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  allow JavaCalls in HotSpotConstantPool.callSystemExit

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Changes:
  - all: https://git.openjdk.org/jdk/pull/16383/files
  - new: https://git.openjdk.org/jdk/pull/16383/files/f47527a7..b7181d70

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16383&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16383&range=04-05

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/16383.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16383/head:pull/16383

PR: https://git.openjdk.org/jdk/pull/16383